1. Field of the Invention
The present invention relates to optical apparatus provided with optical thin films and, more particularly, to optical apparatus having good wavelength characteristics across a wide wavelength range. Further, the present invention concerns exposure apparatus provided with the optical apparatus, and an exposure method.
2. Related Background Art
Lenses (optical apparatus) are built in the exposure apparatus and other apparatus and it is common practice to lay an antireflection coating on the lenses in order to prevent leakage of light at the lenses. Then attempts have been made to reduce the reflectance to the smallest possible level in the working wavelength region by this antireflection coating.
The conventional optical apparatus as described above, however, had the following problem. Namely, there are not only normally incident rays but also obliquely incident rays at the position where the antireflection coating is disposed on the optical apparatus. These obliquely incident rays correspond to rays reaching the marginal part in the visual field or in the illumination field. The conventional antireflection coatings had the problem that optical energy became lower in the marginal part of the visual field or the illumination field than in the central part. In other words, the conventional antireflection coatings (or reflection-enhancing coatings) involved the problem that there occurred energy transfer unevenness such as transmittance unevenness in the entire visual field, illumination unevenness in the entire illumination field, or the like, for light of a wide wavelength region.
It is, therefore, an object of the present invention to provide optical apparatus capable of achieving good energy transfer characteristics (reflectance characteristics or transmittance characteristics) in the entire visual field or in the entire illumination field for the light of the wide wavelength region, exposure apparatus provided therewith, and an exposure method.
In order to accomplish the above object, the present invention provides optical apparatus in which a thin film with an optical characteristic having wavelength dependence is formed on an optical surface, the optical apparatus comprising a suppressor to suppress the wavelength dependence in a predetermined wavelength band.
By suppressing the wavelength dependence of the thin film such as the antireflection coating or the like by the suppressor, it becomes feasible to achieve good energy transfer characteristics in the entire visual field or in the entire illumination field for the light of the wide wavelength region.
In the optical apparatus of the present invention, the suppressor may be formed on another optical surface different from the aforementioned optical surface in the optical apparatus.
In the optical apparatus of the present invention, the suppressor may be a thin film laid on the another optical surface.
Further, in the optical apparatus of the present invention, the optical characteristic of the thin film is preferably one of the reflectance and the transmittance.
In the optical apparatus of the present invention, a wavelength characteristic of the reflectance of said suppressor is preferably a characteristic having a first region in which the first derivative of the wavelength characteristic is positive, on the short wavelength side and a region in which the second derivative of said wavelength characteristic is negative, in a second region on the longer wavelength side of said first region.
The inventors have conducted extensive and intensive research and found that the conventional thin films of optical apparatus had such a characteristic for the obliquely incident rays in comparison with the characteristic for the normally incident rays that the reflectance on the long wavelength side tended to increase more than the reflectance on the short wavelength side. By employing the above construction of the present invention, the reflectance characteristic of the suppressor becomes one to increase the reflectance on the short wavelength side and decrease the reflectance on the long wavelength side as incidence of rays varies from normal incidence to oblique incidence. This makes it feasible to attain the good energy transfer characteristics in the entire visual field or in the entire illumination field for the light of the wide wavelength region.
In the optical apparatus of the present invention, the predetermined wavelength band is defined preferably in the vicinity to a region between the first region and the second region and more preferably between the first region and the second region.
In the optical apparatus of the present invention, it is preferable to satisfy the following relation:
0.05xe2x89xa6xcex/xcex94xcexxe2x80x83xe2x80x83(1),
where xcex is a center wavelength of the predetermined wavelength band and xcex94xcex is a width of the predetermined wavelength band. In this case, the width xcex94xcex of the predetermined wavelength band is further preferably not less than 10 nm.
In the optical apparatus of the present invention, a maximum angle of incident angles of rays incident to the another optical surface on which said suppressor is provided, may be not less than 5xc2x0.
Exposure apparatus of the present invention is exposure apparatus for transferring a predetermined pattern formed on a mask under illumination, onto a work, the exposure apparatus comprising the above optical apparatus.
Since the exposure apparatus of the present invention incorporates the optical apparatus capable of achieving the good energy transfer throughout the entire visual field or throughout the entire illumination field for the light of the wide wavelength region as described above, an illuminance distribution can be substantially uniform on the work.
The exposure apparatus of the present invention may be one comprising a light source for supplying illumination light, wherein the light source supplies the illumination light including at least two bright lines and wherein the at least two bright lines are in the predetermined wavelength band. In this case, the light source is preferably a discharge lamp and the light source is more preferably a mercury lamp.
The exposure apparatus of the present invention may be one comprising an illumination optical system for illuminating the mask on the basis of illumination light from a light source, and a projection optical system for forming a pattern image of the mask on the work, wherein the suppressor is provided in at least either one of the illumination optical system and the projection optical system.
An exposure method of the present invention is characterized in that the pattern on the mask is formed on the work by use of the exposure apparatus of the present invention.
Since the exposure method of the present invention employs the optical apparatus capable of achieving the good energy transfer throughout the entire visual field or throughout the entire illumination field for the light of the wide wavelength region as described above, the illuminance distribution can be substantially uniform on the work.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.